How to change the email and username in gitbash


I have to change my email and username where i have initially given .Please help me how to change it.

i have given

git config --global"abc" 

git config --global""

how to chnage te given name and email.

Thanks in advance

Note that updating your name and e-mail in Git bash only has effect on commits made after the update. Commits that already have been made, will not be updated with the new details.